Sarcoidosis is a rare disease that can affect any organ in the body. It is characterized by the buildup of immune-system (fights off infection in the body) cells in organs. These cells form small groups called granulomas, which lead to inflammation of the surrounding tissue. Sarcoidosis most commonly affects the lung and the lymph nodes (part of the immune system). The signs usually include shortness of breath, fever, dry cough, and chest pain. Other signs in many patients can include redness and painful lumps on the skin, reduced eyesight, joint pain, and rarely, nervous system damage. Sarcoidosis commonly affects young and middle-aged adults.